FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Where it initially occurred in the Rowland County area about a week ago, the major bollworm moth flight has continued to increase to a two-night average capture of almost 1,000 moths for the past 5 days. Next door in Scotland County, the July 17 light trap moth counts of 274 and 492 in Laurel Hill and Johns, respectively, indicate that moderate to high bollworm pressure continues in that area. The flight continues moderate to high in Duplin County with Wednesday and Friday light trap counts of 149 and 238. The 10 percent terminal egg threshold has essentially been met in most or all fields across this area. Some fields have received their second pyrethroid treatment.
The bollworm moth flight is now occurring in Lenior County (4, 24, 97, and 175 moths captured on July 13, 14, 15 and 16, respectively), and started on July 16 in the Craven, Jones and Onslow counties. Likewise, the bollworm moth flight appears to be underway in Sampson County in the Clinton area, and points south. This flight line probably means that newly-emerged bollworm moths are also present in Pamlico, Pender, Bladen, Columbus and Cumberland counties. The egg threshold has probably been met or will soon be met in the above areas. Scouts should also be aware of increases of newly-emerged bollworm moths in and around cotton fields as indications that the flight is probably underway in those areas.
This weekend or early next week the bollworm moth flight can be expected to begin in Wayne, Greene, Pitt, Beaufort, Harnett, and Johnston (southern) counties, and perhaps in Beaufort and Hyde counties. Twice per week scouting is recommended in all of the above areas where the moth flight is suspected. The egg threshold is also being met in some areas further north, for example in a part of Wilson county.
Bollworm moths continue to be the predominant species in the flights to this point, although some budworm moths are now being reported. I will try to keep an eye on this. Control often becomes more difficult if budworms begin to make up a significant proportion of the bollworm/budworm larval population.
It would appear that the anticipated bollworm pressure will likely translate into higher costs for insect control than last year. Even with yield prospects down in a number of cotton fields, the expected size of these bollworm moth flights and the probable heavy egg lay should probably be treated with insecticide aggressively at the start, with subsequent judgements about additional treatments based upon potential yield returns.
B.t. cotton must be monitored carefully for bollworms, stink bugs and their damage, and fall armyworms. Because B.t. cotton often returns significant yield increases following treatment of low levels of bollworms and/or stink bugs, thresholds could well be met quickly this year if the high bollworm moth pressure continues, particularly if stink bugs and fall armyworms become an additional factor. Be aware of that the rarely-reached egg threshold (100 eggs per 100 terminals or 20 eggs per 100 fruit, which is 10-fold the egg threshold for conventional cotton) could be reached in some fields in the coming weeks. European corn borers and tobacco budworms will not become established on B.t. cotton at economically-significant levels.
Be alert for signs of European corn borer moth activity in and around cotton fields. Pheromone and light traps continue to capture moderate levels of moths. Rank cotton (not too common at this point), the presence of European corn borer moths in and around fields and field borders (especially on grass heads), and earlier stem penetrations often signal the possibility of an economically-significant infestation developing. Pyrethroid insecticide treatments for bollworms usually hold European corn borer damage to low levels unless the flights and egg mass deposition extends beyond the bollworm protection window (see the July 10 issue of the North Carolina Pest News, Cotton Information or the Cotton Insect Scouting Guide).
Aphids are present in many cotton fields, and at high levels in
some fields. Predators, parasites and a parasitic fungus are our
primary and most effective line of defense against cotton aphids.
If most cotton plants have colonies large enough to cause wilting
of the plant in the morning hours and no aphid mummies or fungus
are observed, a small test spray may be indicated. This confined
spray should tell the producer if the aphids in those effected
cotton fields are resistant to the test chemical. Beneficial
organisms most often work better than insecticides against cotton
aphids. The wasp which causes the aphid mummies can often
withstand several pyrethroid applications, and the parasitic fungus
is unaffected by insecticides.
Web page last updated on July 20, 1998 by Stephen J. Toth, Jr..
